Various types of tubbings are known to the art of tunnel or shaft construction. Tubbing typically comprises a lining of metal around the shaft of an excavation, such as a shaft of a mine or tunnel. Tubbing segments are assembled on site into tubbing rings, joined by bolts and typically compressed with concrete. The tubbing rings are assembled and joined together to form a housing to provide support to the excavated tunnel or shaft and also to provide a degree of watertightness. Housings made from tubbings therefore find particularly useful application in excavations of difficult mining and geological conditions, including tunnels or excavations that have been constructed or sunk though water bearing strata. Tubbing is typically used to enable those who sink shafts and underground tunnels to penetrate unstable formations or water bodies with safety. Tubbing can be used to make, support and seal mineshaft walls and underground tunnels such as subway tunnels, ventilation shafts and the like.
Tubbing segments used in these sorts of applications are typically reinforced steel or cast iron. The individual steel or cast iron segments are assembled into rings by bolting and the rings so formed are in turn bolted onto adjacent rings to form the housing. The tubbing has vertical flanges through which holes are drilled to allow tubbing segments to be bolted to one another and horizontal flanges through which holes are drilled to allow adjacent tubbing rings to be bolted to one another. The segments and rings are typically bolted using tubbing bolts which are generally known to the art.
Space outside the tubbing and between the tubbing and the excavated shaft or tunnel can be grouted or concreted to add strength and improve watertightness to the tunnel. Grout or concrete is applied in the space between the tubbing and excavated tunnel to form a barrier to water inflow, reducing water inflow to the tunnel through the tubbing joints. Typically, grout applied behind tubbing is cement-based. However, the grout applied can be one or more other types, including polymer based or latex based grout.
In these applications of grouting, where the aim is essentially to fill the void between the tubbing and the tunnel cavity, a first stage of the operation is to fill the bulk of the cavity with large volume of material. Particularly if cementitious grout is used, the grout can settle during introduction, causing channels to form, through which water can still migrate. These channels can sometimes at least in part be remedied by second stage grouting which can seal these channels and simultaneously lock any tubbing lining into the surrounding ground. If necessary, grout can be applied via injection through an array of holes drilled out from the tubbing and into the surrounding strata.
Despite these measures, water inflow into a tunnel constructed with use of tubbing can still occur. One problem that persists is leakage that can penetrate into the tunnel or into space between tubbing rings via leaks in or at the bolts that hold tubbing segments and/or tubbing rings together, or which attach flanges of tubbing to the tunnel wall. Since these bolts are part of the final structure of the tubbing and hence the constructed tunnel, they remain in place for the duration of the life of the tunnel and so leakage through these points can lead to a persistent problem that diminishes the integrity of the tunnel or shaft.
How large a problem this leaking turns out to be depends on the amount of leakage through each bolt join and the number of bolt joins in any tubbing housing that develop a leak. The seriousness of the problem also depends on what is deemed to be an acceptable level of water inflow into the tunnel. The acceptable level of water inflow in any tunnel situation will depend on a number of factors, including the purpose of the tunnel. For example, a tunnel excavated for purposes of installing a subway will require less inflow of water than a mine shaft. However, even in the context of different mine excavations, the nature of the mineral involved may dictate that the mine be essentially completely dry. Further, some tunnel situations may require longevity of grouting application in preventing water inflow. In these situations, standard cement-based grouting techniques may be less than optimal. There is therefore an existing need for improvements in preventing or reducing leaks in tunnels or shafts constructed using tubbing, particularly in preventing or reducing leaks that occur through joins in tubbing segments or between tubbing rings.